A substantial amount of the materials used for carpet underlay are produced from rebonded flexible organic foam and preferably rebonded polyurethane foam. Rebonded foam is generally obtained by a process which broadly consists of applying a binder to small particles of foam, compressing the resultant mix and allowing the binder to fully cure.
In manufacturing rebonded foam and particularly polyurethane foam, foam particles are placed in a suitable mixing container, such as a ribbon blender, where the foam particles are subjected to vigorous mixing. As the foam pieces are being agitated, a binder is sprayed into the mixing container. After the foam and binder are thoroughly blended, the mixture is transferred to a mold and compressed or is transferred to continuously moving compression conveyors. In either case, the mixture is held in the compressed state until the resultant product is dimensionally stable. The resultant product may then be fabricated into whatever shape is required for the particular intended end use application. Typical of the continuous process is that described in U.S. Pat. No. 3,726,624.
The instant invention relates to the molding process noted above. When utilizing polyurethane foam, the so-called "molding" process generally produces a cylindrical roll or log of rebonded polyurethane foam. These rolls or logs are then cut to sheet materials. The molding procedures known to date suffer many disadvantages common to batch operations including high cost and relatively low production rates. Additionally, uniformity of density in the resultant sheets is difficult to achieve due to density variations within the log itself. Due to the lack of uniformity, significant amounts of scrap are produced. It is additionally extremely difficult to obtain reproducible and consistent products. Characteristic of this type of process are those described in U.S. Pat. Nos. 3,517,414; 3,114,722; 3,300,421; 3,401,128; 3,485,711; 3,503,840; 3,717,597; 3,730,917; 3,772,210; and 3,894,973.
One process available commercially consists broadly in the following steps: filling a mold with a mixture of foam particles and binder, compressing the mixture, curing the binder while the mixture is in the compressed state, drilling a hole in the cured product, and removing the mold from the product. One of the most serious problems with this process is the variations in density of the final product resulting in significant foam loss during subsequent processing.